The present invention relates to magnetic systems, and more particularly to an improved method and structure for providing electrical contact to a TMR element.
Tunneling magnetoresistive (TMR) elements are of increasing interest for a variety of applications. FIG. 1 depicts a conventional method 10 for providing a conventional TMR element. FIGS. 2A through 2D depict the conventional TMR element 30 during formation. Referring to FIGS. 1 and 2A-2D, the layers for the conventional TMR element 30 are formed, via step 12. Step 12 includes forming ferromagnetic layers separated by a nonmagnetic insulating layer. One of the ferromagnetic layers is a pinned layer, having its magnetization pinned in placed, typically using an antiferromagnetic layer. The other ferromagnetic layer is a free layer, having its magnetization free to move in response to an external field. A capping layer, for example Ta is also typically provided. A PMGI layer is formed on the TMR layer, via step 14. A layer of photoresist is formed on the PMGI layer and patterned, via step 16. Typically, the resist is patterned by photolithography. The PMGI is then undercut, via step 18. Step 18 is performed by selectively dissolving a portion of the PMGI under the resist. FIG. 2A depicts the conventional TMR element 30 after step 18 has been performed. Ferromagnetic layers 32 and 36 of the TMR element 30 are separated by a thin insulating layer 34. An antiferromagnetic layer 31 is also depicted. Thus, the conventional TMR element 30 is a conventional bottom pinned TMR element. A capping layer 37 is also typically present. The insulating layer 34 is thin enough to allow charge carriers to tunnel through the insulating layer 34. Based upon the difference between the magnetizations of the ferromagnetic layers 32 and 36 the resistance of the conventional TMR element 30 changes. Also shown are the photoresist 40 and the PMGI 38. The PMGI 38 has been undercut below the edge of the photoresist 40. Thus, bi-layer structure is formed by the PMGI 38 and the photoresist 40.
The conventional TMR element 30 is then defined, via step 20. Typically, step 20 is accomplished using a reactive ion etch or by ion milling. FIG. 2B depicts the conventional TMR element 30 after step 20 has been performed. Because of the bi-layer structure formed by the undercut PMGI 38 and the resist 40, the conventional TMR element 30 has the desired shape and size. A dielectric film is then deposited to partially encapsulate the conventional TMR element 30, via step 22. FIG. 2C depicts the conventional TMR element 30 after step 22 has been preformed. The dielectric film having portions 42A, 42B and 42C has been deposited. Because of the presence of the PMGI 38 and the photoresist 40, the dielectric film 42A and 42B covers only the side portions of the conventional TMR element 10. Also shown is dielectric film 42C that covers the photoresist 40. The photoresist 40, PMGI 38 and dielectric film 42C are then removed, via step 24. FIG. 2D depicts the conventional TMR element 30 after removal of the PMGI 38 and the photoresist 40. Because the top of the conventional TMR element 30 is now exposed, electrical contact can then be made to the conventional TMR element 30.
Although the conventional method 10 functions, one of ordinary skill in the art will readily recognize that the method 10 may not adequately function for smaller sizes of the conventional TMR element 30. As the size of the conventional TMR element 30 decreases, for example below 0.5 microns, undercutting the PMGI 38 in step 18 becomes problematic. In particular, the PMGI 38 may wash away entirely instead of being selectively dissolved. Because the PMGI 38 is completely removed instead of being undercut, the conventional TMR element 30 cannot be defined.
Accordingly, what is needed is a structure and method for providing a smaller TMR element as well as for providing electrical contact to such a smaller TMR element. The present invention addresses such a need.
The present invention provides a method and structure for providing a tunneling magnetoresistive (TMR) element. The method and structure comprise providing a TMR layer that includes a first magnetic layer, a second magnetic layer and a first insulating layer disposed between the first magnetic layer and the second magnetic layer. The method and structure also comprise providing a first material and a protective layer. The first material allows electrical contact to be made to the tunneling magnetoresistive layer and is disposed above the tunneling magnetoresistive layer. The first material is capable of being undercut by a plasma etch without exposing a portion of the tunneling magnetoresistive layer under the remaining portion of the first material. The second protective layer covers a portion of the tunneling magnetoresistive sensor and a portion of the first material. In one aspect, the method and structure also include providing a second material disposed between the tunneling magnetoresistive layer and the first material. The second material allows electrical contact to be made to the tunneling magnetoresistive layer through the first material and the second material. The second material is both resistant to removal by the plasma etch and provides protection for the TMR element.
According to the structure and method disclosed herein, the present invention provides a TMR element that can be made smaller and to which electrical contact can be made.